Quality of malaria microscopy in 12 district hospital laboratories in Tanzania.

Background: The WHO recommendation for parasitological diagnosis of malaria wherever possible is challenged by evidence of poor-quality microscopy in African hospitals but the reasons are not clear.

Methods: All 12 of the busier district hospital laboratories from three regions of Tanzania were assessed for quality of the working environment and slide readers read 10 reference slides under exam conditions. Slides that had been routinely read were removed for expert reading.

Results: Of 44 slide readers in the study, 39 (88.6%) correctly read >90% of the reference slides. Of 206 slides that had been routinely read, 33 (16%) were judged to be unreadable, 104 (51%) were readable with difficulty, and 69 (34%) were easily readable. Compared to expert reading of the same slide, the sensitivity of routine slide results of easily readable slides was 85.7% (95% confidence interval: 77.4-94.0), falling to 44.4% (95% confidence interval: 34.5-54.4) for slides that were 'readable with difficulty'.

Conclusions: The commonest cause of inaccurate results was the quality of the slide itself, correction of which is likely to be achievable within existing resources. A minority of slide readers were unable to read slides even under ideal conditions, suggesting the need for a 'slide reading licence' scheme.